For example, Patent Document 1 discloses a conventional vehicle seat reclining device. As shown in FIG. 6, this device includes a base plate 91 that is fixed to a seat cushion and a pair of guide portions 93 provided on the base plate 91. The guide portions 93 are placed in parallel with each other to form a guide groove 92 that extends in a radial direction. The device includes a tooth plate 94 that is fixed to a seat back. The tooth plate 94 has formed therein a sectoral recess 95 centered at a hinge, and has a tooth portion 96 formed on an arcuate inner circumferential surface of the recess 95. Moreover, in the guide groove 92, a tooth member 97 is placed to be movable forward and backward with respect to the tooth portion 96 of the tooth plate 94. The tooth member 97 is provided with a tooth portion 98 that is engageable with the tooth portion 96 of the tooth plate 94.
The tooth member 97 engages with a cam that is urged by an urging member in a direction of rotation. The tooth member 97 is urged by the urging member in a forward direction so that its tooth portion 98 engages with the tooth portion 96 of the tooth plate 94 via the cam. Rotation of the cam against an urging force of the urging member by a manipulation lever causes the tooth member 97 to move backward so that its tooth portion 98 and the tooth portion 96 of the tooth plate 94 disengage from each other. This makes it possible to adjust and maintain the angle of inclination of the seat back with respect to the seat cushion at a desired angle suitable for a seated occupant by selectively permitting or restricting relative rotation of the base plate 91 and the tooth plate 94.
Further, Patent Document 1 proposes the following configuration, in which the tooth member 97 has side portions 99 formed in parallel with the guide portions 93. The guide portions 93 have greater thicknesses at tip end portions that are close to the tooth portion 96 of the guide portions 93, thereby having close contact portions 101 and 102, respectively, formed to protrude toward and contact the side portions 99 of the tooth member 97. This reduces the area of contact between the guide portions 93 and the side portions 99 of the tooth member 97, so that the tooth member 97 is held between the guide portions 93 to such an extent as to be movable forward and backward with respect to the tooth portion 96 of the tooth plate 94. Moreover, even when the seat back receives load, a gap in a direction of rotation centered at a center shaft can be maintained at the minimum, which reduces rattling of the seat back.